that's your converter, which has a built-in battery charger.
the fan is probably running constantly, because your battery is dead, low or bad.
do you have a battery disconnect switch? if you don't keep it plugged into shore power, the parasitic power drains will empty a battery in a few days.
i'm betting that the battery is bad, if you've kept it hooked up to shore power.
and Zoe the Wonder Dog(R.I.P.)
'07 Roo 23SS pushing an '07 Chevy Avalanche
Equalizer WDH and Prodigy BC